The administration of muscarinic anticholinergic drugs to humans produces a complex pattern of behavioral alterations often described as including changes in mood, arousal, and perception. Studies with experiemental animals injected with these drugs have revealed changes both in the ability to withhold responses and to discriminate stimulus changes. These two classes of behavioral changes in animals may parallel the effect of these drugs on arousal and perception in humans. The goal of the proposed project is to develop a behavioral technique for use with the rat to simultaneously and independently measure changes in response bias and stimulus sensitivity produced by these drugs. This technique, involving a discriminated avoidance procedure analyzed by the Theory of Signal Detection, will then be used in conjuncton with intracranial administraion of anticholinergics to hopefully separate the neural substrates of these two classes of behavioral change. This technique may prove useful for the neuro-behavioral analysis of other psychoactive drugs as well. The results should also contribute to the understanding of the neural mechanisms involved in bigilance and stimulus control.